Process for producing compound semiconductor using an amorphous nucleation site

ABSTRACT

A process for producing a compound semiconductor comprises applying a crystal forming treatment on a substrate having a free surface comprising a nonnucleation surface (S NDS ) with smaller nucleation density and a nucleation surface (S NDL ) arranged adjacent thereto having a sufficiently small area for a crystal to grow only from a single nucleus and a larger nucleation density (ND L ) than the nucleation density (ND S ) of said nonnucleation surface (S NDS ), by exposing the substrate to either of the gas phases: 
     (a) gas phase (a) containing a starting material (II) for feeding the group II atoms of the periodic table and a starting material (VI) for feeding the group VI atoms of the periodic table and 
     (b) gas phase (b) containing a starting material (III) for feeding the group III atoms of the periodic table and a starting material (V) for feeding the group V atoms of the periodic table, thereby forming only a single nucleus on said nucleation surface (S NDL ) and permitting a monocrystal of the compound semiconductor to grow from said single nucleus, characterized in that 
     a semiconductor junction is formed in said monocrystal by feeding a starting material (Dn) for feeding a dopant for controlling to one electroconduction type and a starting material (Dp) for feeding a dopant for controlling to the electroconduction type opposite to said electrocondition type with change-over to one another into said gas phase, during said crystal forming treatment.

This application is a continuation of application Ser. No. 174,511 filedMar. 28, 1988, abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for producing a compoundsemiconductor having a desired conduction type region and asemiconductor device obtained by using the same.

2. Related Background Art

In the prior art, for fromation of pn junction in compoundsemiconductors, the liquid phase growth method, the MOCVD method, theMBE method have been practiced. Among them, the liquid phase growthmethod has been primarily practiced, and therefore description thereofis set forth below by referring to an example.

Liquid phase growth utilizes slow-cooled epitaxial growth, namelydifference in the conduction type layers deposited due to difference intemperature.

FIG. 18A shows the carrier concentration distribution near the pnjunction of a compound semiconductor formed by the above prior artmethod. FIG. 18B shows the change in carrier concentration correspondingto the relationship between solution temperature and time. Initially,when the solution temperature is T₁, the region near the substrate is aconductive layer having a high carrier concentration of n-type, andn-type carrier concentration is reduced as the temperature is lowered.And, at the point of the temperature of T₂, the n-p reversal temperatureis reached and pn junction is formed. When slow cooling is furthercontinued, p-type layer will grow while becoming higher concentration,until growth is completed at the temperature T₃ by departing thesubstrate from the solution.

When growth is performed by use of this method, as is apparent from FIG.18A, the carrier concentration near the pn junction becomes lower,whereby there is the problem that when a device is formed, its responsespeed becomes delayed.

Also, although it is possible to grow similarly a compound semiconductorcrystal by the MOCVD method or the MBE method as previously mentioned,the above methods have not yet been technically established, and cannotbe said to be sufficiently reliable.

Further, since the crystal growth by use of the three kinds of methodsas mentioned above is epitaxial growth, there is the drawback that anexpensive compound semiconductor substrate such as GaAs, etc. must beused as the substrate.

Besides, as to the structures of grown layers, in all of the prior artexamples, the pn junction faces will become in parallel to the substratesurface.

SUMMARY OF THE INVENTION

The present invention has been accomplished in view of the above points,and its primary object is to provide a process for producing a compoundsemiconductor which has solved the problems as described above of theprior art.

Another object of the present invention is to provide a process forproducing a novel compound semiconductor which can produce a compoundsemiconductor easily and with good reproducibility and bulkproductivity.

Still another object of the present invention is to provide a processfor producing a compound semiconductor which can provide a compoundsemiconductor capable of forming a semiconductor electronic deviceimproved in response speed with good reliability.

Yet another object of the present invention is to provide a process forproducing a compound semiconductor, which comprises applying a crystalforming treatment on a substrate having a free surface comprising anonnucleation surface (S_(NDS)) with a smaller nucleation density and anucleation surface (S_(NDL)) arranged adjacent thereto having asufficiently small area for a crystal to grow only from a single nucleusand a larger nucleation density (ND_(L)) than the nucleation density(ND_(S)) of said nonnucleation surface (S_(NDS)), by exposing thesubstrate to either of the gas phases:

(a) gas phase (a) containing a starting material (II) for feeding thegroup II atoms of the periodic table and a starting material (VI) forfeeding the group VI atoms of the periodic table and

(b) gas phase (b) containing a starting material (III) for feeding thegroup III atoms of the periodic table and a starting material (V) forfeeding the group V atoms of the periodic table, thereby forming only asingle nucleus on said nucleation surface (S_(NDL)) and permitting amonocrystal of the compound semiconductor to grow from said singlenucleus, characterized in that a semiconductor junction is formed insaid monocrystal by feeding a starting material (Dn) for feeding adopant for controlling to one electroconduction type and a startingmaterial (Dp) for feeding a dopant for controlling to theelectroconduction type opposite to said electroconduction type withchange-over to one another into said gas phase, during said crystalforming treatment.

Yet still another object of the present invention is to provide aprocess for producing a compound semiconductor, which comprises applyinga crystal forming treatment on a substrate having a free surfacecomprising a nonnucleation surface (S_(NDS)) with a smaller nucleationdensity and a nucleation surface (S_(NDL)) arranged adjacent theretohaving a sufficiently small area for a crystal to grow only from asingle nucleus and a larger nucleation density (ND_(L)) than thenucleation density (ND_(S)) of said nonnucleation surface (S_(NDS)), byexposing the substrate to either of the gas phases:

(a) gas phase (a) containing a starting material (II) for feeding thegroup II atoms of the periodic table and a starting material (VI) forfeeding the group VI atoms of the periodic table and

(b) gas phase (b) containing a starting material (III) for feeding thegroup III atoms of the periodic table and a starting material (V) forfeeding the group V atoms of the periodic table, thereby forming only asingle nucleus on said nucleation surface (S_(NDL)) and permitting amonocrystal of the compound semiconductor to grow from said singlenucleus, characterized in that a semiconductor junction is formed insaid monocrystal by feeding a starting material (Dn) for feeding adopant for controlling to one electroconduction type while changing theintroduced amount of said starting material (Dn) with the lapse of time.

Again another object of the present invention is to provide asemiconductor device by use of the compound semiconductor obtained bythe above production process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the relationship between the size of the nucleusr_(c) and the free energy G.

FIGS. 2A and 2B illustrate schematically the selective depositionmethod.

FIGS. 3A-3D illustrate diagramatically the steps of a first example ofthe formation process for crystals according to the present invention.

FIGS. 4A and 4B are perspective views in FIGS. 3A and 3D.

FIGS. 5A-5D are diagrams of the formation steps of the crystal showing asecond example of the crystal forming process of the present invention.

FIGS. 6A-6D are diagrams of the formation steps showing a third exampleof the process for forming the crystal of the present invention.

FIGS. 7A and 7B are perspective views of FIGS. 6A and 6D.

FIGS. 8A-8E are diagrams of the formation steps of the crystal showing afirst embodiment of the present invention.

FIG. 9 illustrates the pnp junction transistor using a monocrystalobtained in accordance with the present invention.

FIGS. 10A and 10B illustrate another junction type semiconductor deviceusing a monocrystal obtained in accordance with the present invention.

FIGS. 11A-11C and 12A-12E are diagrams of the steps of a secondembodiment of the present invention.

FIG. 13 illustrates the substrate for crystal formation used in thepresent invention.

FIGS. 14A and 14B illustrate another semiconductor device using amonocrystal obtained in accordance with the present invention.

FIGS. 15A-15J are diagrams of the formation steps of the LED device inone example of the present invention.

FIGS. 16A-16I are diagrams of the formation steps of the LED device inanother example of the present invention.

FIG. 17 illustrates the X-Y matrix twodimensional planer LED deviceusing a monocrystal obtained by the present invention.

FIG. 18A shows the carrier concentration distribution near the pnjunction of a compound semiconductor formed by the above prior artmethod and FIG. 18B shows the change in carrier concentrationcorresponding to the relationship between solution temperature and time.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the present invention, a desired conduction type region is formed bychanging the growth conditions during crystal growth of a compoundsemiconductor on the nucleation surface (S_(NDL)) by utilizingnucleation density difference (ΔND).

First, for better understanding of the present invention, as the relatedbasic technology, general thin film forming process of a metal or asemiconductor is to be explained.

When the deposition surface (crystal growth surface) is of a materialdifferent in kind from the flying atoms, particularly an amorphousmaterial, the flying atoms will be freely diffused on the substratesurface and reevaporated (eliminated). And, as the result of collisionmutually between the atoms, a nucleus is formed, and when the nucleusreaches the size rc (=-2σ_(o) /gv) or more at which its free energy Gbecomes the maximum (critical nucleus), G is reduced and the nucleuscontinues to grow stably three-dimensionally and become shaped in anisland. The nucleus with a size exceeding rc is called "stable nucleus"and in the basic description of the present invention hereinbelow,"nucleus" unless otherwise specifically noted indicates the "stablenucleus".

Also, of the "stable nucleus", one with small r is called "initialnucleus". The free energy G formed by formation of the nucleus isrepresented by:

    G=4πf(θ)(σ.sub.o r.sup.2 +1/3·gv·r.sup.3)

    f(θ)=1/4(2-3 cosθ+cos.sup.2 θ)

where

r: radius of curvature of nucleus

θ: contact angle of nucleus

gv: free energy per unit volume

σ_(o) : surface energy between nucelus and vacuum.

The manner in which G is changed is shown in FIG. 1. In the same Figure,the curvature of radius of the stable nucleus when G is at the maximumvalue is rc.

Thus, the nucleus grows to become shaped in an island, and further growsuntil contact mutually between islands proceeds, giving rise tocoalescence in some cases, finally forming via a network structure acontinuous film to cover completely the substrate surface. Through suchprocess, a thin film is deposited on the substrate.

In the deposition process as described above, the density of the nucleusformed per unit area of the substrate surface, the size of the nucleusand the nucleation speed are determined depending on the state of thesystem of deposition, and particularly the interaction between theflying atoms and the substrate surface substance is an important factor.Also, a specific crystal direction grows in parallel to the substratedepending on the anisotropy relative to the crystal face of theinterfacial energy at the interface between the deposited substance andthe substrate, and when the substrate is amorphous, the crystaldirections within the substrate plane are not constant. For this reason,a grain boundary is formed by collision mutually between nuclei orislands. Particularly, in case of collision mutually between islandswith certain sizes or greater, coalescence will occur, leading directlyto formation of a grain boundary. The grain boundary formed can bemigrated with difficulty in the solid phase, and therefore the grainsize is determined at that point.

Next, the selective deposition film forming method for formingselectively a deposited film on the deposition surface is to bedescribed. The selective deposition film forming method is a method inwhich a thin film is selectively formed on the substrate by utilizingthe difference between the materials in the factors influencingnucleation in the thin film forming process such as surface energy,attachment coefficient, elimination coefficient, surface diffusionspeed, etc.

FIGS. 2A and 2B illustrate schematically the selective deposition filmforming method. First, as shown in FIG. 2A, on the substrate 1, a thinfilm 2 comprising a material different in the above factors from thesubstrate 1 is formed at a desired portion on the substrate 1. And, whendeposition of a thin film comprising an appropriate material isperformed according to appropriate deposition conditions, it becomespossible to cause a phenomenon to occur such that the thin film 3 willgrow only on the free surface of the thin film 2 without growth on thefree surface of the substrate 1. By utilizing this phenomenon, the thinfilm 3 self-alignmently formed can be permitted to grow, whereby thelithographic step by use of a resist as practiced in the prior art canbe omitted.

As the materials which can be deposited by such selective depositionfilm forming method, there may be included, for example, SiO₂ as thesubstrate 1, Si, GaAs, silicon nitride as the thin film 2, and Si, W,GaAs, InP, etc. as the thin film 3 to be deposited.

The II-VI group compound crystal can be grown on a Si substrate, or aII-VI group compound substrate, and cannot be grown on SiO₂ substrate asis known in the art. However, by implanting ions of the group IIIelements (atoms), the group V elements (atoms), or ions of the group IIelements (atoms), the group VI elements (atoms) of the periodic table ona SiO₂ substrate, the nucleation density (ND) at the ion implantedportion can be enhanced to make the difference (ΔND) in nucleationdensity from the SiO₂ substrate sufficiently large, whereby selectivedeposition of the group II-VI compound can be effected.

The III-V group compound crystal can be grown on a Si substrate, a III-Vgroup compound substrate, and cannot be grown on SiO₂ substrate as isknown in the art. However, by implanting ions of the group III elements(atoms), the group V elements (atoms), or ions of the group II elements(atoms), the group VI elements (atoms) of the periodic table on a SiO₂substrate, the nucleation density (ND) at the ion implanted portion canbe enhanced to make the difference (ΔND) in nucleation density from SiO₂substrate sufficiently large, whereby selective deposition of the groupIII-V compound can be effected.

Also, it is possible to add a different material having largernucleation density (ND_(L)) to the material surface having smallernucleation density (ND_(S)) such as SiO₂ substrate and form selectivelya deposited film by utilizing the nucleation density difference (ΔND).

The present invention utilizes the selective deposition method based onsuch nucleation density difference (ΔND), and a nucleation surfacecomprising a material which has sufficiently larger nucleation densitythan the material forming the deposition surface (crystal formationsurface) and is different from the latter material is formedsufficiently finely so that only a single nucleus may grow, whereby asingle crystal is grown selectively only from such a fine nucleationsurface.

Since the selective growth of single crystal is determined depending onthe electron state of the nucleation surface, particularly the state ofdangling bond, the material with lower nucleation density for formingthe nucleation surface (e.g. SiO₂) is not required to be a bulkmaterial, but the nucleation surface may be formed on the surface of anydesired material substrate.

Next, the outline of the process for forming crystals according to thepresent invention is described in detail by referring to the drawings.

FIGS. 3A-3D illustrate diagramatically the steps of a first example ofthe formation process for crystals according to the present invention,and FIGS. 4A and 4B are perspective views in FIGS. 3A and 3D.

First, as shown in FIG. 3A and FIG. 4A, on the substrate 4 comprisinghigh melting point glass, quartz, alumina, ceramics, etc., a thin film 5with small nucleation density enabling selective nucleation[nonnucleation surface (S_(NDS))] is formed, and a material differentfrom the material forming the thin film 5 with small nucleation densityis thinly deposited thereon, followed by patterning by lithography, etc.to form sufficiently finely a nucleation surface comprising a differentmaterial (S_(NDL)) (or called "Seed") 6, thus obtaining a substrate forcrystal formation. However, the size, the crystal structure and thecomposition of the substrate 4 may be as desired, and it may be also asubstrate having a functional device previously formed thereon by theconventional semiconductor technique. Also, the nucleation surface(S_(NDL)) 6 comprising a different material is, as described above,inclusive of Se, As modified regions formed by ion implantation on thethin film 5 The nucleation surface is the surface on which substantiallyonly single nucleus is formed and is constituted of an amorphousmaterial.

Next, by selecting appropriate deposition conditions, a monocrystal of athin film material is formed only on the nucleation surface (S_(NDL)) 6.That is, the nucleation surface (S_(NDL)) 6 is required to be formedsufficiently finely to the extent that only a single nucleus may beformed. The size of the nucleation surface (S_(NDL)) 6, which depends onthe kind of the material, may be several microns or less. Further, thenucleus grows while maintaining a single crystal structure to become asingle crystal grain 7 shaped in an island as shown in FIG. 3B. For theisland-shaped single crystal grain 7 to be formed, it is desirable todetermine the conditions for crystal forming treatment so that nonucleation may occur at all on the free surface of the thin film 5.

The island-shaped monocrystalline grain 7 further grows whilemaintaining the monocrystalline structure with the nucleation surface(S_(NDL)) 6 as the center (lateral overgrowth), whereby the thin film 5can be partially or wholly covered therewith as shown in FIG. 3C(monocrystal 7A).

Subsequently, the surface of the monocrystal 7A is flattened by etchingor polishing to form a monocrystal layer 8 on the thin film 5, on whicha desired device can be formed, as shown in FIG. 3D and FIG. 4B.

Thus, since the thin film 5 constituting the nonnucleation surface(S_(NDS)) is formed on the substrate 4, any desired material can be usedfor the substrate 4 which is the supporting member. Further, in such acase, even if the substrate 4 may be one having a functional device,etc. formed by the conventional semiconductor technique, amonocrystalline layer 8 can be easily formed thereon.

In the above example, the nonnucleation surface (S_(NDS)) was formedwith the thin film 5, but of course as shown in FIGS. 5A-5D a substratecomprising a material with small nucleation density (ND) enablingselective nucleation may be used as such, and the monocrystalline layermay be formed similarly with provision of the nucleation surface(S_(NDL)) at any desired position.

FIGS. 5A-5D are diagrams of the formation steps of the crystal showing asecond example of the crystal forming process according to the presentinvention. As shown in FIGS. 5A-5D, by forming a nucleation surface(S_(NDL)) 6 comprising a material with larger nucleation density (ND)sufficiently finely on a substrate 9 comprising a material with asmaller nucleation density (ND) enabling selective nucleation, toprovide a substrate for crystal formation and a monocrystalline layer 8can be formed on said substrate similarly as in the first example.

FIGS. 6A-6D are digrams of the formation steps showing a third exampleof the process for forming the crystal according to the presentinvention, and FIGS. 7A and 7B are perspective views of FIGS. 6A and 6D.

As shown in FIG. 6A and FIG. 7A, on an amorphous insulating materialsubstrate 11, nucleation surfaces (S_(NDL)) 12-1, 12-2 are arrangedsufficiently small with a material different from the above substrate 11with a distance l therebetween. The distance l may be set equal to thesize of the single crystal region required for formation of, forexample, a semiconductor device or a group of devices or greater thanthat.

Next, by selecting appropriate crystal forming conditions, only onenucleus of the crystal forming material is formed on only the nucleationsurfaces (S_(NDL)) 12-1, 12-2. That is, the nucleation surfaces(S_(NDL)) 12-1, 12-2 are required to be formed to sufficiently finesizes (areas) to the extent that only a single nucleus may be formed.The sizes of the nucleation surfaces (S_(NDL)) 12-1, 12-2, which maydiffer depending on the kind of the material, may be preferably 10 μm orless, more preferably 5 μm or less, optimally 1 μm or less. Further, thenucleus grows while maintaining a monocrystalline structure to becomeisland-shaped single crystal grains 13-1, 13-2 as shown in FIG. 6B. Forisland-shaped monocrystal grains 13-1, 13-2 to be formed, as alreadymentioned, it is desirable to determine the conditions for crystalforming treatment so that no nucleation will occur at all on othersurfaces than the nucleation surfaces (S_(NDL)) on the substrate 11.

The crystal orientations of the island-shaped single crystal grains13-1, 13-2 in the normal direction of the substrate 11 are constantlydetermined such that the interface energy of the material is mademinimum. For, the surface or the interface energy has anisotropydepending on the crystal face. However, as already mentioned, thecrystal orientation within the substrate plane in an amorphous substratecannot be determined.

The island-shaped monocrystalline grains 13-1, 13-2 further grow tobecome monocrystals 13A-1, 13A-2, whereby adjoining monocrystals 13A-113A-2 contact mutualy each other as shown in FIG. 6C, but since thecrystal orientation within the substrate plane is not constant, acrystal grain boundary 14 is formed in the middle portion between thenucleation surfaces (S_(NDL)) 12-1 and 12-2.

Subsequently, single crystals 13A-1, 13A-2 grow three-dimensionally, butthe crystal face with slower growth speed will appear as the facet. Forthis reason, flattening of the surfaces of monocrystals 13A-1, 13-2 isperformed by etching or polishing, and further the portion of the grainboundary 14 is removed, to form the thin films 15-1, 15-2, 15 of singlecrystals containing no grain boundary in shape of lattice as shown inFIG. 6D and FIG. 7B. The sizes of the monocrystalline thin films 15-1,15-2, 15 are determined by the distance l between the nucleationsurfaces (S_(NDL)) 12 as described above. That is, by definingappropriately the formation pattern of the nucleation surfaces (S_(NDL))12, the position of the grain boundary can be controlled to formmonocrystals with desired sizes at a desired arrangement.

The present invention utilizes the crystal formation process asdescribed above by referring to FIG. 3A to FIG. 7B by way of example.

In the present invention, in the above crystal formation process,crystal forming treatment is performed in gas phase, and either one of:

(a) gas phase (a) containing a starting material (II) for feeding thegroup II atoms of the periodic table and a starting material (VI) forfeeding the group VI atoms of the periodic table and

(b) gas phase (b) containing a starting material (III) for feeding thegroup III atoms of the periodic table and a starting material (V) forfeeding the group V atoms of the periodic table, is selected as the gasphase, and a semiconductor junction is formed in the crystal of thecompound semiconductor formed by feeding into the selected gas phase astarting material (D) for feeding a dopant to control the conductiontype as mentioned in the semiconductor field thereof with change-over oftheir kind corresponding to the kind of conduction type.

The typical crystal of the compound semiconductor obtained in theprocess for producing the compound semiconductor of the presentinvention is the so-called II-VI group compound semiconductor crystaland the III-V group compound semiconductor crystal.

As the respective starting materials to be used in the productionprocess of the present invention, there may be included specifically thefollowing compounds as suitable examples.

As the starting material (II) for feeding the group II atoms of theperiodic table (abbreviated as "the group II atoms"), for necessity tobe fed into gas phase, those which are under gaseous state or readilygasifiable are preferred.

These points can be said to be applicable similarly to the startingmaterial (VI) for feeding the group VI atoms of the periodic table(abbreviated as "the group VI atoms"), the starting material (III) forfeeding the group III atoms of the periodic table (abbreviated as "thegroup III atoms"), the starting material (V) for feeding the group Vatoms of the periodic table (abbreviated as "the group V atoms") and thestarting material (D) for feeding dopant.

As the starting material (II), there may be included dimethyl zinc,diethyl zinc (Zn(C₂ H₅)₂), dimethyl cadmium (Cd(CH₃)₂), diethyl cadmium,dipropyl cadmium (Cd(C₃ H₇)₂), dibutyl cadmium (Cd(C₄ H₉)₂), dimethylmercury (Hg(CH₃)₂), diethyl mercury (Hg(C₂ H₅)₂), etc., and as thestarting material (VI) hydrogen sulfide (H₂ S), selenium hydride,dimethyl selenium, diethyl selenium (Se(C₂ H₅)₂), dimethyl diselenide(CH₃ SeCH₃), dimethyl tellurium (Te(CH₃)₂), diethyl tellurium (Te(C₂H₅)₂), etc. By combination of these starting materials (II) and (VI),monocrystals of II-VI group compound semiconductors such as ZnS, ZnTe,CdS, CdTe, HgSe, ZnO, etc. and mixed crystal compound monocrystals ofthese can be selectively formed on the nucleation surface (S_(NDL)).

In the case of obtaining III-V group compound semiconductor crystals, byuse of trimethyl indium In (CH₃)₃ as the starting material (III) andphosphine PH₃ as the starting material (V), InP monocrystals can beformed selectively on an amorphous substrate, and also AlSb monocrystalsby use of trimethyl aluminum Al(CH₃)₃ as the starting material (III) andstibine SbH₃ as the starting material (V). By combination of therespective starting materials as described above, monocrystals of eitherone of GaP, GaSb, InAs, InSb, AlAs and AlP can be selectively grown, andfurther any desired combination of mixed crystal III-V group compoundmonocrystals can be selectively grown.

As the starting materials (III), the above compounds having methyl groupare not limitative, but it is also possible to use compounds havingethyl group, propyl group, butyl group, isobutyl group such as triethylgallium Ga(C₂ H₅)₃, tripropyl indium In(C₃ H₇)₃, tributyl gallium Ga(C₄H₉)₃, triisobutyl aluminum Al(CH₃)₂ CHCH₂, etc.

FIRST EMBODIMENT

FIGS. 8A-8E illustrate a first embodiment of the present invention.

First, a nonnucleation surface 802 is formed on a substrate 801. Next, anucleation surface 803 is formed sufficiently finely so that a singlenucleus may be formed. This size may be preferably 10 μm or less, morepreferably 5 μm or less, as described above. Optimally it is 1 μm orless. The materials for forming such nonnucleation surface 802 andnucleation surface 803 may differ depending on the crystalline materialconstituting the monocrystals to be formed. In the case of formingmonocrystals of GaAs, an amorphous material such as silicon nitride,aluminum oxide, etc. may be used as the material for forming thenucleation surface 803, and silicon oxide, etc. may be used as thematerial for forming the nonnucleation surface 802. Also, as shown inFIG. 8A, without formation of a film on the substrate 801, for example,As ions may be implanted into the SiO₂ film in an excessive amount, andthe modified region thus formed may be used as the nucleation surface803. In the case of producing a II-VI group compound semiconductor suchas ZnS, ZnSe, CdSe, etc., silicon oxide, etc. may be used as thematerial for forming the nonnucleation surface 802, while as thematerial for forming the nucleation surface 803, an amorphous materialsuch as silicon nitride, aluminum oxide, etc. may be employed. Also,similarly as in the case of III-V group, without formation of a film, Seions may be implanted into the SiO₂ film in an excessive amount, and themodified region thus formed may be used as the nucleation surface 803.

FIG. 8A shows a substrate having a nonnucleation surface 802 withsmaller nucleation density thus formed, and a nucleation surface 803which is arranged adjacent to said nonnucleation surface 802, has anarea sufficiently small for a crystal to grow only from a single nucleus804 and has a nucleation density greater than said nonnucleation surface802.

In the present invention, by applying a crystal forming treatment to thesubstrate, a single nucleus 804 is formed and a monocrystal is permittedto grow from said single nucleus. At the stage of forming said singlenucleus 804, there is no problem whether the dopant may be added or not.The crystal forming treatment of the present invention has the step ofcrystal formation in which a starting material (Dn) for feeding a dopantfor controlling to one conduction type is added to the gas phase forcrystal forming treatment and the step of crystal formation in which thestarting material (Dp) for feeding a dopant for controlling to theopposite conduction type is added to the above gas phase.

For example, in practicing the present invention for formation ofcrystals of III-V group compound semiconductor, for controlling theconduction type to p-type, the atoms of the group II of the periodictable such as Zn, Be, etc. can be used.

For controlling the conduction type to n-type, the atoms of the group IVof the periodic table such as Si, Ge, Sn, etc. or the atoms of the groupVI of the periodic table such as S, Se, Te, etc. can be used as then-type dopant.

In the case of practicing the present invention for formation ofcrystals of a II-VI group compound semiconductor, for controlling theconduction type to the p-type, the atoms of the group V of the periodictable such as P, N, As, etc. can be used as the p-type dopant, while forcontrolling to the n-type, the atoms of the group III of the periodictable such as B, Al, Ga, etc., or the atoms of the group VII of theperiodic table such as F, Cl, etc. can be used as the n-type dopant.These dopants can be incorporated into the crystals by feeding thestarting material (D) for feeding dopant into the gas phase for carryingout crystal forming treatment during the crystal forming treatment.

In the present invention, by feeding the starting material (Dn) forfeeding the n-type dopant and the starting material (Dp) for feeding thep-type dopant into the gas phase containing the starting materials forfeeding the atoms which become the matrix of the crystals to be formed,namely, the above starting materials (II) and (VI) in the case of II-VIgroup compound semiconductor, with switchover to one another, asemiconductor junction is formed in the crystals formed.

The starting materials (D) similarly as in the case of the startingmaterials (II), (VI), (III) and (V), may be suitably selected from amongthose which are gaseous or readily gasifiable and will not give badinfluence to the crystals formed.

Specifically, the starting material (Dn) may include, for the II-VIgroup compound semiconductor, B₂ H₆, AlR₃, GaR₃, InR₃, HF, Hcl and thelike; for III-V group compound semiconductor, H₂ S, SR₂, H₂ Se, SeR₂,TeR₂, SiH₄, GeH₄, SnR₄ and the like as suitable ones. The startingmaterial (Dp) may include, for II-VI group compound semiconductor, PH₃,NH₃, AsH₃, RAsH₃ and the like; for III-V group compound semiconductor,ZnR₂, BeR₂ and the like as suitable ones. In those formulas, Rrepresents an alkyl group, preferably CH₃ or C₂ H₅.

As shown in FIG. 8B, after a single nucleus 803 is formed on thenucleation surface 803, or during formation of the single nucleus, byadding a desired amount of the starting material (D) for feeding thedopant for controlling the conduction type in addition to the startingmaterial (M) for feeding the atoms which become the matrix of thecrystals formed into the gas phase for crystal forming treatment, amonocrystalline semiconductor region 805 with a desired conduction typecan be formed.

For example, when a starting material (Dp) for feeding the p-type dopantis employed as the starting material (D) for feeding the dopant, thesemiconductor region 805 becomes the p-type semiconductor region, whileif the starting material (Dn) for feeding the n-type dopant is employed,the semiconductor region 805 becomes the n-type semiconductor region. Inthe figure, the semiconductor region 805 is shown as the p-type. At thestage, when the semiconductor region 805 has grown to a desired size, byswitching the starting material (D) for feeding the dopant to thestarting material for feeding the dopant of the conduction typedifferent from the conduction type of the semiconductor region 805, asemiconductor region 806 different in the conduction type from thesemiconductor region 805 can be formed continuously around thesemiconductor region 805.

For example, when the semiconductor region 805 is the p-type, by addinga desired amount of the starting material (Dn) for feeding the n-typedopant into the gas phase for crystal forming treatment, the conductiontype of the semiconductor region 807 can be made the n-type. Thus, byswitching over the kind of the starting material (D) for feeding dopantat appropriate times as desired, a semiconductor junction can be formedin the monocrystal of the compound semiconductor formed. FIG. 8D showsthe state in which pn junction is formed, and FIG. 8E shows the state inwhich pnp junction is formed.

As shown in FIG. 8E, by flattening by removing the upper portion of themonocrystal of the compound semiconductor having pnp junction formed, asemiconductor monocrystalline region having the pnp junction in theplane direction of the substrate 801 can be made on the substrate 801 asshown in FIG. 9. By providing electrodes 901, 902 and 903 on the uppersurfaces of the p-type region 805a, the n-type region 806a and thep-type region 807a of the semiconductor monocrystalline region thusformed, respectively, a pnp type transistor can be obtained.

SECOND EMBODIMENT

Similarly as in the case of the first embodiment, after a compoundsemiconductor monocrystal having pnp junction is formed as shown in FIG.8E, the upper end portion of the monocrystal is removed to be flattenedsimilarly as in the case shown in FIG. 9 (FIG. 10A).

Then, by providing electrically separating regions 1005, 1006 in thevertical direction on the main surface of the substrate 1001, asemiconductor region having pnpnp junction and a semiconductor regionhaving pnp junction are formed. Its upper plane view is shown in FIG.10B. As shown in FIG. 10B, the semiconductor region having pnpn junctionis constituted of the p-type semiconductor region 1004a, the n-typesemiconductor region 1003a, the p-type semiconductor region 1002a, then-type semiconductor region 1003b and the p-type semiconductor region1004b. The semiconductor region having pnp junction is constituted ofthe p-type semiconductor region 1002b, the n-type semiconductor region1003c, the p-type semiconductor region 1004c.

By providing electrodes respectively on the upper plane surfaces of thesemiconductor regions electrically separated similarly as in the case ofFIG. 9, the semiconductor device having pnpnp junction and thesemiconductor device having pnp junction can be formed at the same timeon the substrate 1001.

As the method for electrical separation, there may be employed themethod for cutting spacially by etching, etc. or the method in which apredetermined semiconductor region is made higher in resistance by ionimplantation, etc. In the case when the compound semiconductormonocrystal is GaAs, as the ions to be implanted, Cr ions can beimplanted to form partially a region with increased resistance.

The present invention is described in detail by referring to Examples.

EXAMPLE 1

FIGS. 11A-11C and FIGS. 12A-12E are diagrams showing the preparationsteps of LED with GAP compound monocrystalline semiconductor.

First, according to FIGS. 11A-11C, a substrate for growing a compoundmonocrystalline semiconductor crystal was formed. FIG. 11A:

On the surface of the glass substrate 1101, SiO₂ layer 1102 of about1000 Å was formed by the normal pressure CVD method by use of SiH₄ andO₂. FIG. 11B:

A photoresist layer 1103 was applied and patterning was effected so asto make a window portion 1104 of 2 μm square (generally it may be someμm square or less). And, by use of an ion implanter, P³⁻ ions wereimplanted in an amount of 1×10¹⁶ /cm² onto SiO₂ layer 1102 (this portionbecomes the nucleation surface with high nucleation density and ishereinafter called seed portion). FIG. 11C:

After the photoresist layer 1103 was peeled off, the substrate 1101surface was subjected to heat treatment in PCl₃ atmosphere at 1050° C.for 10 minutes, to obtain a substrate for GaP selective nucleus growthsuch that the region 1105 implanted with P³⁻ exists at a certain portionon SiO₂ layer 1102.

FIGS. 12A-12E are diagrams of steps for forming a planar type LED deviceregion by growing continuously GaP monocrystal from p-type to n-type onthe above substrate. The respective steps are as described below. FIG.12A:

On the substrate obtained in FIG. 11C, a monocrystalline nucleus 1106 ofGaP was formed by use of the MOCVD method. As the starting materials,trimethylgallium (TMG) and PH₃ were employed. PH₃ was decomposed by thehot cracking method immediately before introduction and fed into thereaction tube. The TMG/PH₃ molar ratio was 1.5 and the diluting gas wasH₂. At this time, in order to make p-type, 0.02% of (C₂ H₅)₂ Zn wasmixed. FIG. 12B:

The above monocrystalline nucleus was homoepitaxially grown to form ap-type GaP semiconductor region 1106. FIG. 12C:

When p-type GaP monocrystalline region 1106 grew to a certain size, thedoping gas was switched to H₂ Se (0.05%), to grow a n-type GaPsemiconductor region 1107. FIG. 12D:

When a GaP semiconductor monocrystalline island with a double layerstructure of p-type and n-type was prepared, as shown in FIG. 12Dmechanical polishing was performed in parallel to the substrate so thatthe p-type semiconductor region 1106 was exposed to effect flattening ofthe upper portion of the monocrystal. On the right side of FIG. 12Dthere is shown the state as viewed from above the substrate. FIG. 12E:

On the flattened GaP monocrystal, electrodes were attached to form a LEDdevice. As the electrode 1108 of the p-type region 1106, an alloy ofAg-In-Zn (8:1:1) was used, which was vapor deposited and subjected toheat treatment at 650° C. in Ar atmosphere for 5 minutes. On the otherhand, as the electrode 1109 of the n-type region 1107, an alloy of Au-Ni(20:1) was used, which was vapor deposited and subjected to heattreatment at 550° C. in H₂ atmosphere for 2 minutes.

The LED device of GaP thus obtained exhibited a light emission spectrumhaving a peak near 560 nm, similarly as the GaP prepared by use of amonocrystalline wafer.

EXAMPLE 2

In this example, the seed portion (corresponding to 1105 in FIG. 11C)was formed by thin film patterning. In Example 1, the seed portion 1105was obtained by implanting P³⁻ ions into the fine portion in the crystalgrowth region, but in this example, the seed portion 1303 was obtainedby depositing an Al₂ O₃ thin film and further subjecting the Al₂ O₃ filmto fine patterning. The details are as described below.

(a) Similarly as in Example 1, an SiO₂ layer 1302 was deposited on aglass substrate 1301.

(b) Next, by use of the ion plating method, an Al₂ O₃ film was depositedto about 300 Å. That is, by means of an arc discharge type ion platingdevice, after evacuation to 10⁻⁵ Torr, O₂ gas was introduced to 1×10⁻⁴-3×10⁻⁴ Torr, and an Al₂ O₃ film was deposited under the conditions ofan ionization voltage 50 V (output 500 W), a substrate potential of -50V, and a substrate temperature of 400° C.

(c) As shown in FIG. 13, the Al₂ O₃ film was subjected to patterning to2 μm by use of the photolithographic technique to form the seed portion1303. The etchant was H₃ PO₄ :HNO₃ :CH₃ COOH:H₂ O=16:1:2:1 (40° C.).

(d) After the photoresist was peeled off, an LED of GaP was prepared byemploying the same steps as in Example 1. The LED device obtainedexhibited light emission having a peak at around 560 nm similarly as inExample 1.

EXAMPLE 3

In this example, GaAs was grown. Also for GaAs, TMG and AsH₃ were usedas the starting gases, and p-type and n-type could be freely controlledby use of Si as the n-type dopant and Be as the p-type dopant similarlyas in growth of GaP.

EXAMPLE 4

In this example, a MES type FET as shown in FIGS. 14A, 14B was formed.In the MES type FET shown in FIG. 14A, a three-layer structure wasformed in the order of n⁺, n, n⁺ and electrodes were attached as shownin FIG. 14A after mechanical flattening. In the MES type FET shown inFIG. 14B, a double layer structure was formed in the order of n⁺, n and,after mechanical flattening, the n⁺ region was separated into twoinsulated parts, followed by attachment of the electrodes as shown inFIG. 14B. In FIGS. 14A, 14B, G represents Schottky gate electrode, Ssource electrode and D drain electrode. The compound semiconductormonocrystal used was GaP.

EXAMPLE 5

FIGS. 15A- FIG. 15J are preparation steps showing an example of GaPlight emission diode. FIG. 15A:

On the surface of the substrate 1501, SiO₂ layer 1502 of about 1000 Åthickness was deposited by the CVD method by use of SiH₄ and O₂. Thesputtering method may be used in place of the CVD method. FIG. 15B:

Patterning was effected with a photoresist film provided on the SiO₂layer 1502, followed by masking with the window portion of 1 μm² beingremained. And, by use of an ion implanter, P³⁻ ions were implanted in anamount of 1×10¹⁶ /cm² into the SiO₂ layer 1502. FIG. 15C:

At the portion of the SiO₂ layer 1502 corresponding to the windowportion of the photoresist, a seed portion 1503 implanted with P ionswas formed. FIG. 15D:

In a PCl₃ atmosphere, heat treatment was performed at 900° C. for 10minutes, and then a p-type semiconductor monocrystalline island 1504 ofGaP was grown by use of the MOCVD method. As the starting materials,trimethylgallium (TMG) and PH₃ were employed. PH₃ was decomposed by thehot cracking method immediately before introduction and fed into thereaction tube. The molar ratio of TMG to PH₃ was 2:1 and the dilutinggas was H₂. The reaction pressure was normal, and the substratetemperature was 850° C.

In the starting material for feeding the p-type dopant, 0.02% ofdiethylzinc (DEZn) was mixed. FIG. 15E and FIG. 15F:

When the p-type GaP 1504 grew to a desired size, the doping gas waschanged from DEZn to selenium hydride (H₂ Se) to grow n-type GaP 1505.H₂ Se was mixed TO 0.05%. FIG. 15G:

The upper portion of the monocrystalline islands 1504, 1506 wereflattened by mechanical polishing. FIG. 15H:

After preparation of a negative pattern with a resist, Au-Ni (20:1) wasvapor deposited to 3000 Å. The resist was dissolved by use of a solventto lift off unnecessary portions, thereby forming an n-side electrode1506. Further, the electrode was heated in H₂ atmosphere at 550° C. for2 minutes. FIG. 15I:

An SiO₂ film 1507 was deposited to 4000 Å by the sputtering method, anda contact hole 1508 to the n-layer was formed by use of thephotolithographic technique. FIG. 15J:

Ag-In-Zn (8:1:1) was deposited to 6000 Å by vapor deposition, subjectedto patterning with a photoresist and then a p-side electrode 1509 wasformed according to the dry etching method by use of CCl₂ F₂. Further,the electrode was heated in Ar atmosphere at 650° C. for 5 minutes.Thus, a LED device was prepared.

When a transparent material such as SiO₂ is used as the substrate 1501,light emission occurs from the bottom of the device through thesubstrate 1501. On the contrary, when the substrate 1501 is opaque asalumina, by making the electrodes 1506, 1509 except for the contactportions transparent electrodes such as of ITO, light emission can beeffected from the direction before of the substrate 1501 (upper part inthe drawing).

EXAMPLE 6

FIGS. 16A- FIG. 16I are diagrams of the steps for preparation of a GaNlight emission diode which is one of MIS type LED. The respective stepsare described below. FIG. 16A:

An SiO₂ film 1602 was deposited to about 1000 Å on the surface of thesubstrate 1601 according to the CVD method by use of SiH₄ and O₂. FIG.16B:

Next, by use of the ion plating method, an Al₂ O₃ film was deposited to300 Å. That is, by means of an arc discharge type ion plating device,after evacuation to 10⁻⁵ Torr, O₂ gas was introduced to 1-3×10⁻⁴ Torr,and Al₂ O₃ was deposited under the conditions of an ionization voltage50 V (output 500 W), a substrate potential of -50 V, and a substratetemperature of 400° C. Then, resist patterning, and followed bypatterning to 1.5 μm with an etchant (H₃ PO₄ :HNO₃ :CH₃ COOH:H₂O=16:1:2:1, 40° C.) were effected, thereby forming a seed portion 1603of Al₂ O₃. FIG. 16C:

In PCl₃ atmosphere, heat treatment was conducted at 950° C. for 10minutes, and then a monocrystalline island 1604 of n-type GaN was grownby the MOCVD method. As the starting gases, trimethylgallium (TMG) andammonia (NH₃) were employed, with the TMG/NH₃ molar ratio being made120, and the diluting gas H₂. The reaction pressure was made normal, andthe substrate temperature 1000° C. FIG. 16D:

The grown monocrystalline island 1604 of GaN was flattened by mechanicalpolishing. FIG. 16E and FIG. 16F:

After patterning with a photoresist 1605, Zn²⁺ ions 1606 were implantedin an amount of 1×10¹⁶ /cm², and heated in H₂ atmosphere at 900° C. for5 minutes to form an insulating layer 1607 (high resistance GaN layer).FIG. 16G:

After preparation of a negative pattern with a resist, In-Al was vapordeposited to 2000 Å. Next, the resist was dissolved to lift offunnecessary portions, thereby forming an electrode 1608. FIG. 16H:

SiO₂ was deposited to 3000 Å by the sputtering method, and a contacthole 1610 to the insulating layer 1607 was formed by use of thephotolithographic technique. FIG. 16I:

In-Al was vapor deposited to 5000 Å, followed by patterning to form anelectrode 1611 on the insulating layer 1607 side. As the etchant, FeCl₃:HCl:H₂ O=2:3:10 was employed. When the MIS type LED of GaN, thusprepared was subjected to light emission actuation, good emissioncharacteristics were exhibited.

The selective nucleation LED preparation steps of GaP, GaN as describedabove can be practiced not only by the above MOCVD method, but also bythe MBE method and the LPE method. Also, they are applicable also forother compound semiconductor materials other than GaP and GaN.

FIG. 17 is a plane view of a LED array comprising a plural number of thep-n junction type LED as previously explained as Example 5 arranged on asingle substrate. 1701 shown in this Figure is a n-type GaP crystal,1702 a p-type GaP crystal, 1703 and 1704 are electrodes (see FIGS.15G-15J).

Also, it is possible to form an LED array by use of the MIS type LEDexplained as Example 6 other than the p-n junction type LED.

Further, by arranging LED's having a plural number of emission colorswithin the LED array, for example, by arranging LED's of R, G and Bemission, a color image displayer can be also constituted. Here, it issuitable to use GaAsP as the R (red color) emitting LED, GaP as the G(green color) emitting LED and GaN as the B (blue color) emitting LED.

As described above, according to the present invention, enlargement ofarea and low cost of the substrate can be realized by the technique forbuilding up selectively a compound semiconductor crystal in shape ofislands at any desired position of any desired substrate. Also, the pnjunction face obtained by practicing the present invention is exposed aspositioned in the direction approximately vertical to the substratesurface, and therefore the steps of device formation can be simplifiedby reducing the number of photopatterning during device formation.

The effects of the present invention may be more specifically enumeratedas follows.

(1) Because of selective nucleus growth on any desired substrate, thesubstrate is not limited to expensive compound semiconductor substrates.

(2) Because a crystal can be grown only on the desired position, it ispossible to completely effect insulating separation mutually between thedevices during formation of devices.

(3) Since the pn junction face obtained by practicing the presentinvention is not in parallel to the substrate but exposed in thedirection vertical thereto, the photoetching steps, etc. during deviceformation can be omitted to a great extent.

As another effect, a LED device can be easily prepared on any desiredbase substrate at any desired position.

By doing so, a large scale display device which is hither to prepared byhibridization of a large number of LED devices can be easily prepared asthe monolithic constituton.

Also, it becomes possible to prepare a one-dimensional light source ortwo-dimensional (plane emission) light source by a LED array withmonolithic constitution.

Further, according to the present invention, since it becomes alsopossible to form LED on a substrate such as ceramics, etc., reduction ofproduction cost can be effected.

We claim:
 1. A process for producing a compound semiconductor, whichcomprises applying a crystal forming treatment on a substrate having afree surface comprising a non-nucleation surface (S_(NDS)) with asmaller nucleation density and an amorphous nucleation surface (S_(NDL))arranged adjacent thereto having a sufficiently small area so as to forma single nucleus from which a single crystal is grown and a largernucleation density (ND_(L)) than the nucleation density (ND_(S)) of saidnonnucleation surface (S_(NDS)) so as to form only a single nucleus fromwhich a single crystal is grown, by exposing the substrate to either ofthe gas phases:(a) gas phase (a) containing a starting material (II) forfeeding the group II atoms of the periodic table and a starting material(VI) for feeding the group VI atoms of the periodic table; and (b) gasphase (b) containing a starting material (III) for feeding the group IIIatoms of the periodic table and a starting material (V) for feeding thegroup V atoms of the periodic table, thereby forming a single nucleus onsaid nucleation surface (S_(NDL)) and permitting a monocrystal of thecompound semiconductor to grow only from said single nucleus,characterized in that a semiconductor junction is formed in saidmonocrystal by feeding a starting material (Dn) for feeding a dopant forcontrolling to a first electroconduction type and a starting material(Dp) for feeding a dopant for controlling to a second electroconductiontype opposite to said first electroconduction type with change-over toone another into said gas phase, during said crystal forming treatment.2. A process for producing a compound semiconductor according to claim1, wherein said crystal growth treatment is performed according to theMOCVD method.
 3. A process for producing a compound semiconductoraccording to claim 1, wherein said nucleation surface (S_(NDL)) isformed internally of said nonnucleation surface (S_(NDS)).
 4. A processfor producing a compound semiconductor according to claim 1, whereinsaid nucleation surface (S_(NDL)) is formed in a plural number assectionalized.
 5. A process for producing a compound semiconductoraccording to claim 1, wherein said nucleation surface (S_(NDL)) isformed in a plural number as sectionalized regularly.
 6. A process forproducing a compound semiconductor according to claim 1, wherein saidnucleation surface (S_(NDL)) is formed in a plural number assectionalized irregularly.
 7. A process for producing a compoundsemiconductor according to claim 1, wherein said nucleation surface(S_(NDL)) is formed in the shape of a lattice.
 8. A process forproducing a compound semiconductor according to claim 1, wherein themonocrystal formed on the nucleation surface (S_(NDL)) is grown in thedirection of the nucleation surface (S_(NDL)) beyond said nucleationsurface (S_(NDL)).
 9. A process for producing a compound semiconductoraccording to claim 4, wherein the monocrystal grown from the eachnucleation surface (S_(NDL)) is grown to the size to be adjacent to theadjoining nucleation surface (S_(NDL)).
 10. A process for producing acompound semiconductor according to claim 1, wherein said nucleationsurface (S_(NDL)) is formed of a material which is modified from thematerial for producing said nonnucleation surface (S_(NDS)).
 11. Aprocess for producing a compound semiconductor according to claims 1,wherein said compound semiconductor is a binary system compoundsemiconductor.
 12. A process for producing a compound semiconductoraccording to claim 1, wherein said compound semiconductor is a mixedcrystal compound semiconductor.
 13. A process for producing a compoundsemiconductor, which comprises applying a crystal forming treatment on asubstrate having a free surface comprising a nonnucleation surface(S_(NDS)) with a smaller nucleation density and an amorphous nucleationsurface (S_(NDL)) arranged adjacent thereto having a sufficiently smallarea so as to form a single nucleus from which a single crystal is grownand a larger nucleation density (ND_(L)) than the nucleation density(ND_(S)) of said non-nucleation surface (S_(NDS)), so as to form asingle nucleus from which a single crystal is grown by exposing thesubstrate to either of the gas phases;(a) gas phase (a) containing astarting material (II) for feeding the group II atoms of the periodictable and a starting material (VI) for feeding the group VI atoms of theperiodic table; and (b) gas phase (b) containing a starting material(III) for feeding the group III atoms of the periodic table and astarting material (V) for feeding the group V atoms of the periodictable, thereby forming a single nucleus on said nucleation surface(S_(NDL)) and permitting a monocrystal of the compound semiconductor togrow only from said single nucleus, characterized in that asemiconductor junction is formed in said monocrystal by feeding astarting material (Dn) for feeding a dopant for controlling to oneelectroconduction type while changing the introduced amount of saidstarting material (Dn) with the lapse of time.
 14. A process forproducing a compound semiconductor according to claim 1, wherein saidsubstrate is constituted of an amorphous material.
 15. A process forproducing a compound semiconductor according to claim 14, wherein saidamorphous material is SiO₂.